The present invention pertains primarily to self-locking threaded fastener means, and more particularly to threaded fastener means having self-locking properties provided by the use of an interference creating material on the threaded portion thereof.
The following cited references are believed to be representative of the state of the art:
______________________________________ U.S. Pat. No. Inventor Issued ______________________________________ 2,321,414 Parker June 8, 1943 2,686,342 D'Eustachio August 17, 1954 2,741,288 Johnson April 10, 1956 2,928,446 James et al March 15, 1960 3,022,197 Jedlicka February 20, 1962 3,093,177 Villo June 11, 1963 3,146,142 Maly August 25, 1964 3,294,139 Preziosi December 27, 1966 3,437,541 Cooper et al April 8, 1969 3,498,352 Duffy March 3, 1970 3,554,258 Duffy January 12, 1971 3,568,746 Faroni et al March 9, 1971 3,737,355 Epstein et al June 5, 1973 3,784,435 Bagheri et al January 8, 1974 3,818,525 Bedi June 25, 1974 ______________________________________
and U.S. application Ser. No. 737,558, filed Nov. 1, 1976, assigned to Federal Screw Works.
Generally, threaded fastener means having self-locking properties provided by the use of an interference creating material on the threaded portion thereof, have consisted of fasteners coated in part with soft metal, rubber, nylon, polyester or the like. These fastener means, some of which are known as patch bolts, function by providing an interference fit between two mating threaded surfces, thereby eliminating or substantially reducing relative movement of the two mating surfaces.
Such fastener means should be distinguished from thread-locking materials which typically create a permanent adhesive bond between the two mating threaded surfaces and usually are formulated using thermosetting adhesives such as epoxies, etc. Patch-type fasteners, on the other hand, do not create an adhesive bond between the two mating surfaces, and usually are made using heat-bonded thermoplastic materials. Patch-type fasteners must be capable of exhibiting the yield necessary for an interference fit but yet provide adequate resistance to relative movement of the two mating threaded surfaces. Patch-type fasteners are important in terms of both the on and off directions, and not just the off direction as is the case with thread-locking materials.
An additional requirement encountered in many of the applications of such fastener means is that of multiple usage. Multiple usage is the term used to describe repeated installation and removal of the same fastener. Typical of the industry tests of such properties is the "fifth off" test. This test measures the capability of the same fastener means to be used five times. The fifth off value is the break away torque encountered in an effort to loosen the bolt after the fifth installation. Meeting this requirement but yet maintaining adequate retention has often proved to be a difficult task for many prior art materials since once a material is permanently deformed, its performance as a patch in such a fastener decreases. Repeated deformation aggravates the problem drastically.
For this reason, most present day patch bolts or similar fasteners are made using nylon, a thermoplastic material which exhibits desirable yield properties as well as good interference characteristics when properly positioned. However positioning the nylon patch often presents some problems. For example, if a portion of a threaded bolt is machined out in order to insert a nylon interference creating patch, substantial machining costs are incurred and part of the overall bolt strength is diminished. If, in the alternative, a nylon patch is applied over the threads of a regular bolt by heat-bonding, the more common practice, the bolt must be heated to approximately 600.degree. F. in order to melt on the nylon patch, thereby using a fairly substantial amount of valuable energy as well as often destroying any corrosion resistant coating on the bolt such as phoshate and oil, which breaks down at temperatures in the range of 200.degree.-300.degree. F.
Although alternative materials such as polyesters or some forms of epoxies have been used in an attempt to overcome the problems encountered with nylon, or for that matter, the similar problems that would be encountered with a soft metal or rubber patch, many of these alternatives have proven to be either too expensive as is the case with most polyesters, or have not provided satisfactory application procedures nor adequate overall performance characteristics.
It is a principle object of the present invention therefore to provide an improved self-locking fastener means.
Another object of the present invention is to provide a new and improved fastener product which includes a patch material which is polymerized on the fastener.
It is a further object of the present invention to provide a relatively inexpensive patch material for use on patch bolts which comprises a thermoplastic epoxy adhesive system which is polymerized in situ.
It is yet another object of the present invention to provide a patch material which is energy effective and does not destroy corrosion resistant coatings such as phosphate and oil upon application to the fastener and also has good multiple usage properties.
Other objects, features and advantages of the present invention will become apparent from the subsequent description, and examples, and the appended claims taken in conjunction with the accompanying drawings.